Automatic door operators are used on public buildings and residences to allow for access by the physically disabled or where manual operation of the door may be inconvenient to users. The purpose of a door operator is to open and possibly close a door. A variety of electro-mechanical automatic door operators are known. A typical door operator includes an electric motor and a linkage assembly for operatively coupling the drive shaft of the motor to a door so that the door will be opened and closed when the drive shaft rotates. Activation of the door operator is initiated by means of an electric signal generated in a variety of ways such as, for example, a pressure switch, an ultrasonic or photoelectric presence sensor, motion sensors, radio transmitters, wall switches, and the like. The door may then be closed by the operator motor or with a door closer. Many door closers are mechanically actuated and have a plurality of valves and springs for controlling the varying amounts of force applied to close the door as a function of door angle.
Some door operator systems are provided with clutch mechanisms between the motor and the linkage assembly that enable the door to be moved freely under manual power. Door operators with clutch mechanisms may provide some level of safety when objects are in the door's pathway of movement. Various clutch mechanisms decouple powered opening systems during the closing cycle, which is particularly necessary in the event of an interruption of power supply or when an obstacle is encountered.
When a door operator with a clutch mechanism is used with a mechanical door closer, the features of both a door operator and a full-featured door closer can be available to users of the door. As an example, the automatic opening available with a door operator is available, but in addition, varying amounts of force can be applied to the door by the door closer. Many door closers are designed to apply varying forces to a door as a function of the door angle (i.e., the angle at which the door is open). In this regard, when the door is first opened under manual operation, the door closer is designed to generate a relatively small force, which tends to push the door closed, so that the door closer does not generate significant resistance to the user's efforts to open the door. Many door closers are designed to provide a significant resistive force when the door is pushed open beyond a specific angle, for example, 60 to 70 degrees. This high-force region of operation of the door is often referred to as the “back check” region, and the high force is intended to prevent the back of the door from hitting a wall or stop, possibly causing damage.